Fob Watch

The fob watch is a Time Lord made piece of Technology. It allows a Time Lord to hide there identity and all of there memories within the watch. There is one drawback and that is that you don't remember your past until the fob watch is opened by you.

The watch first appeared in Human Nature to hide the Doctor to hide from the Family of Blood, and he takes on the alias John Smith. He lives a human life and leaves hints to himself - Before putting his memory inside the watch - to remind him of who is truly is.
The watch has been mentioned and seen in the Sounds of Drums and Utopia where we are told the Master has done the same to hide from the great Time War.